Modular stretchable and flexible capacitance sensors for use with electrical capacitance volume tomography and capacitance sensing applications

ABSTRACT

A flexible capacitance sensor having multiple layers for communicating signals to a data acquisition system for reconstructing an image of an area or object located in a subject being sensed, the flexible capacitance sensor having a flexible layer of capacitance plates; a flexible shielding ground layer next to the layer of capacitance plates; a flexible layer of signal traces next to the shielding ground layer, where the layer of signal traces has a plurality of trace lines; and where the capacitance sensor is flexible and adapted to be wrapped around the subject being sensed. The sensor is adapted to communicate signals via the plurality of trace lines to a data acquisition system for providing an image of the area or object between the capacitance plates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/965,636, filed on Aug. 13, 2013 which is herein incorporated byreference in its entirety.

BACKGROUND OF THE INVENTIVE FIELD

Electrical Capacitance Tomography (ECT) is the reconstruction ofmaterial concentrations of dielectric physical properties in the imagingdomain by inversion of capacitance data from a capacitance sensor.

Volume capacitance imaging or ECVT is the direct 3D reconstruction ofvolume concentration or physical properties in the imaging domainutilizing 3D features in the ECVT sensor design.

Adaptive ECVT is an advanced technology that introduces a new dimensioninto 3D sensor design by applying voltages of different frequencies,amplitudes, and/or phases to capacitance plate segments. Adaptivesensors can provide a virtually infinite number of independentcapacitance measurements of the flow field or imaging volume throughwhich high resolution images can be obtained.

ECVT sensors were developed to distribute electric field in threedimensions for reconstruction of dielectric constant distribution in animaging domain.

ECVT sensors can utilize different plate shapes and distributions inmultiple layers to target a volume for imaging.

SUMMARY OF THE EXEMPLARY EMBODIMENTS

The present invention is directed to process tomography and, inparticular, to Electrical Capacitance Volume Tomography (ECVT) andadaptive ECVT sensors and using design techniques for realizingflexible, wearable, stretchable, and modular ECVT sensors.

Dynamic ECVT is a technology that senses measured capacitances betweensensor plates to generate a whole volume image of the region. ECVTtechnology has been applied in providing images of objects movingthrough a pipe for example. ECVT has provided insight into multiphaseflow phenomena in many industrial processes, including pneumaticconveying, oil pipe lines, fluidized beds, bubble columns and many otherchemical and biochemical processes (the multiphase flow often being in acombination of gas, liquid, and solid states). ECVT may also be used forimaging biological processes and tissues.

Capacitance sensing sensors were designed previously to address fixedstructure applications surrounding a dynamic flow component. The designof the present invention includes the integration of all plates,connectors, resistors, and shielding layers into one flexible orstretchable element. The present invention provides an innovative designwith features through which the sensor can be used repeatedly and ondifferent subjects (columns, pipes, organs, or limbs, etc.) throughrelatively simple installations. Specifically, features of the preferredembodiment of the present invention includes the integration of allcomponents of a capacitance sensor into one element (of multiple layers)for handling by users, a modular feature where different platesconfigurations can be easily assembled, a wearable feature where sensorscan be placed by users at different parts of the human body, andstretchable feature where sensors can be expanded in differentdirections. Details of these features are described below.

The integrative design of the present invention combines all elements ofa capacitance sensor into one flexible sheet that can be usedrepeatedly. This flexible sheet in the preferred embodiment containsmultiple layers including the layers of capacitance plates, isolatedsignal traces, ground shielding, isolative/resistive layers betweenconductive layers, a ground layer and low profile connectors forconnecting signal traces to low profile coaxial cables. The plate layercontains design of capacitance sensors aimed at distributing theelectric field in three dimensions. Traces can be separated from eachother by ground to reduce capacitive coupling. The isolative/resistivelayer preferably provides separation between plate layer, signal tracelayer, and shield/ground layer. The resistance provides a path fordischarge of static charges. The shielding ground layer preferablyprovides isolation for the capacitance sensors from outside capacitancecoupling or electric noise. In one embodiment, the low profileconnectors connect the sensor plates to data acquisition system throughsignal traces separated by ground. The ground between traces is aimed atreducing coupling between capacitance plates. The integrative designhere enables capacitance sensors to be used easily for wrapping arounddifferent geometries. It also provides a means for a wearable featurewhere sensors can be placed on the human body in a low profile manner.It also provides a stretchable sensor where sensor elements can beextended for applications where object intended for imaging may changein size or geometry. This integrative approach can be applied for ECVTsensors of different designs and varying number of pates.

The integrative design of the present invention also preferably includesa modular feature where plates fabricated in an integrative approach canbe layered separately for forming an equivalent plate. Such featureenables changing sensor design using modular sensors/plates.

The present invention also preferably includes a stretchable featurewhere sensor plates and layers are fabricated from stretchablematerials. For example, stretchable materials can be a formed ofstretchable flexible boards or flexible metal meshes used forfabricating conductive layers. The flexibility can also be provided byconnecting flexible integrative sensor sections using stretchableconnections. Flexibility can also be provided using conductive spray onstretchable isolative materials (like rubber or elastic material or evenstretchable fabric) to form layers of integrative sensors as explainedabove.

The interactive design of the present invention also preferably includesa combination of traditional solid layered printed circuit boards andflexible or stretchable sensors. Applications of such combinationinclude addressing an object for imaging where a part of it is fixed andanother is expanding.

The integrative design of the present invention also enables measuringof capacitance signals from an Adaptive Electrical Capacitance VolumeTomography (AECVT) sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of an exemplary embodiment will be obtained froma reading of the following detailed description and the accompanyingdrawings wherein identical reference characters refer to identical partsand in which:

FIG. 1 illustrates one embodiment of a flexible integrative sensordesign of the present invention.

FIG. 2 illustrates one embodiment for a sensor with a 2D profile thatshows the different layers in the integrative sensor design depicted inFIG. 1.

FIG. 3 illustrates one embodiment of the sensor with through holes forinterfacing coaxial cables with plates.

FIGS. 4A-E illustrate one embodiment of a 24 channel sensor with layersseparated out individually for illustration.

FIGS. 5A-B illustrate one embodiment of an integrated flexiblecapacitance sensor for ECVT applications.

FIGS. 6A-B illustrate one embodiment of a sensor of the presentinvention configured into one capacitance plate by combining multipleflexible integrative sensors into one equivalent plate.

FIGS. 7A-B illustrate one sensor embodiment for an expandable sensordesign with modular plates.

FIG. 8 illustrates one embodiment of a capacitance sensor of the presentinvention having integrative elements connected using stretchableconnectors.

FIG. 9 illustrates on embodiment of a capacitive sensor of the presentinvention applied on a pre-stretched elastic substrate for forming astretchable ECVT sensor.

FIG. 10 illustrates one embodiment of a modular and removable section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates one embodiment of an integrative sensor design 10 ofthe present invention having with two capacitance plates 12. More platescan be incorporated using the concepts discussed herein to formvirtually any number of sensor configurations of differing shapes andsizes. In the preferred embodiment, the capacitance sensor includesmultiple layers for forming a capacitance sensor. For example, thelayers may include a flexible insulation layer 11, plate layer 14,isolative/resistor layer 16, a shielding ground layer 18, a secondisolative layer 20, a flex signal trace layer 21, an insulation layer 22and a ground layer 24 and connectors integrated into one flexible board10. The plates are preferably made up of conductive material such ascopper (metals), conductive liquid, conductive ink, or conductive spray.In the preferred embodiment, signal traces are used in a separate layerwith ground shielding in between them for isolation of capacitancecoupling. A trace is a conductive line that is imbedded in one of thesensors layers and acts as a means to conduct electric signals fromplates to data acquisition system or from plates to low profileconnectors. Low profile connectors are preferably used for interfacingstrip-lines with coaxial cables for connecting with a data acquisitionsystem for collection sensor readings.

In the embodiment shown in 1, the first insulation layer 11 separatesthe capacitance plates from the object or flow being imaged. The secondlayer is the capacitance plates layer 14. Capacitance plates 12 arepreferably composed of conductive material and are typically made frommetals. In one embodiment, the plates can be made from conductive sprayon a nonconductive layer. The third layer is an isolative layer 16 orresistive layer. This layer separates the plates from the ground layer.The isolative layer can be made resistive so it provides a path todischarge static charges from the plates to the ground. The fourthground layer 18 separates the traces from the plates so they don'tcouple. The fifth layer is again an isolative layer 20 that separatesthe ground layer from the traces layer. The sixth layer is the traceslayer 21. In this layer trace lines 25 are introduced to communicateelectric signals from the plates to data acquisition system or fromplates to low profile connectors. Gaps between traces in this layer arepreferably filled with ground lines to reduce coupling between tracelines. The seventh layer is again isolative 22. The eighth layer is aground layer 24 to shield the sensor from outside interference and fromtrace lines cross-coupling. In the preferred embodiment, all layers areconnected together by a thin layer of adhesive typically used inflexible circuit boards technology. The adhesive layer can also serve asan isolative layer. Another embodiment involves plates, ground, andtraces sprayed or printed on separate layers using conductive spray orink and then layering those layers with insulation between them. Suchseparate layers can be elastic of stretchable materials.

FIG. 2 illustrates one embodiment for a sensor with a 2D profile thatshows the different layers in integrative sensor design depicted in FIG.1.

FIG. 3 illustrates one embodiment of the sensor with through holes 26for interfacing coaxial cables with plates.

FIGS. 4A-E illustrate one embodiment of a 24 channel sensor with layersseparated out individually for illustration. Layers are preferablyseparated by isolative material and they include FIG. 4A plates layer28, FIG. 4B ground layer 30, FIG. 4C signal trace layer 32, and FIG. 4Dground shielding layer 34. The integrated sensor with the layerscombined is shown in the FIG. 4E at 36.

FIGS. 5A-B illustrate one embodiment of an integrated flexiblecapacitance sensor for ECVT applications. FIG. 5A and 5B illustrate thefront and back sides of the fabricated design of FIG. 4E, respectively,with the layers and components of an ECVT sensor integrated in oneflexible circuit.

FIGS. 6A-B illustrate one embodiment of a sensor of the presentinvention configured into one capacitance plate by combining multipleflexible integrative sensors 42 into one equivalent plate. This modularapproach can be used for sensors with multiple plates to form a modularECVT sensor. Modular sections 42 are combined together by connectingplates, traces, and ground of each modular section to another modularsection. Through holes 44 provide means to connecting inner layers of amodular section. For example, a through hole for the trace of a modularsection provides a path directly to the trace and bypassing in-betweenlayers. Modular sections also can be connecting through low profile PCBconnectors where each layer in one modular section is connected to thesame (equivalent) layer of another modular section. Modular sections canalso be connected through stretchable lines for introducing elasticityto the design. An equivalent resulting sensor plate from combiningmodular sections is shown at 46.

FIGS. 7A-B illustrate one sensor embodiment for an expandable sensordesign where modular plates 48 are connected to form an equivalent plate50 where the equivalent plate can change in size by moving modularplates with respect to each other. Through holes 52 provide paths todifferent layers in each modular section. Layers from each modularsection are preferably connected together using corresponding throughholes. Lines used to connect different modular sections can be flexibleor stretchable to provide room for movement of modular plates. Modularplates can be of any shape or size.

FIG. 8 illustrates one embodiment of a capacitance sensor of the presentinvention having integrative elements connected using stretchableconnectors 54 for forming a stretchable ECVT sensor. Here, modularelements similar to ones described in FIG. 7A and 7B are connected usingstretchable lines to connect through holes of different modular sectiontogether. The stretchability of connecting lines renders the new formedplate as stretchable. Stretchable lines can be made of elastic materialsoaked in conductive liquid. Or they can be made of zigzaggedconductors. For example, U.S. Pat. No. 8,469,741 describes examples ofstretchable connectors.

FIG. 9 illustrates on embodiment of a capacitive sensor of the presentinvention applied on a pre-stretched elastic substrate 58 for forming astretchable ECVT sensor. Conductive spray, liquid, or ink is applied topre-stretched layer for forming conductive elements of integrativesensor layers. Elastic substrate can also be soaked in conductive liquidto form conductive parts of any layer in an integrative sensor. Thisconcept can also be applied to the application of the signal traces.

Further details regarding the theory and application of ECVT, sensordesign, image reconstruction, and deployment of an ECVT system are foundin the U.S. Patent Application Publication US 2010/0097374 (applicationSer. No. 11/909,548), the relevant disclosures of which are included byreference thereto as if fully set forth herein.

As depicted in FIGS. 1A and 1B of the U.S. Patent ApplicationPublication US 2010/0097374 referenced herein, an array of electrodes(e.g., capacitance plates) are arranged to form a capacitance sensor. Inone application, this sensor may be placed around a pipe or vent todetect movement within the receptacle to provide imaging data. In aconventional ECVT system, the sensor is made up of capacitance plateswhere the capacitance is measure between a selected pair of plates. Theprinciple of the basic measuring circuit involves connecting one plate(source electrode or sending electrode) of the sensor to a voltage(e.g., Vi) and another plate (detecting electrode or receivingelectrode) to a capacitance measurement circuit.

In the preferred embodiment, the ECVT plates (i.e., electrodes) arecomprised of an array of smaller capacitance segments that may beindividually addressed. The shape of the capacitance segments can bemade up various shapes where each plate can be activated with the sameor different voltages, frequencies, or phase shifts. Segments of eachelectrode are preferably connected together in parallel, with voltagecontrol applied independently to each segment. Segments of interestchosen to form sender or receiver plates can be activated by electronicswitches that open or close to connect a particular segment in parallelwith others chosen in same plate. For example, each segment may beactivated with different amplitudes, phase shifts, or frequency toprovide the desired sensitivity matrix distribution. In one embodiment,the array of selected capacitance segments can form many pairs ofcapacitance electrodes or plates without reducing overall plate size.The capacitance segments can also be joined in different configurationsto provide different designs.

The sensor electronics of the present invention is designed to detectand measure the capacitance for the adaptive ECVT sensor of the presentinvention. For example, the difference in electrical energy stored inthe adaptive ECVT sensor would be measured between an empty state and astate where an object is introduced into the imaging domain (e.g.,between the electrodes). The change in overall energy of the system dueto the introduction of a dielectric material in the imaging domain isused to calculate the change in capacitance related to the dielectricmaterial. The change in capacitance can be calculated from the change instored energy. Sensor electronics can also be designed by placingindividual segment circuits in parallel yielding a summation of currentsrepresenting total capacitance between segments under interrogation. Byindividually addressing the capacitance segments of the electrodes ofthe present invention, electric field distribution inside the imagingdomain can be controlled to provide the desired sensitivity matrix,focus the electric field, and increase overall resolution ofreconstructed images.

FIG. 10 illustrates one embodiment of a modular and removable section 60through which the integrative flexible sensor of the present inventioncan be placed on the outside or on the inside. Removable sections areintroduced as means of placing integrative sensors on fixed structures.

What is claimed is:
 1. A flexible capacitance sensor for communicatingsignals to a data acquisition system for reconstructing an image of anarea or object located in a subject being sensed, comprised of: aflexible layer of capacitance plates; a plurality of trace lines forcommunicating signals from the capacitance plates to the dataacquisition system; wherein the capacitance sensor is flexible andadapted to be wrapped around the subject being sensed; wherein thecapacitance plates in the flexible layer of capacitance plates areindividually addressable; and wherein the sensor is adapted tocommunicate signals to the data acquisition system for use inreconstructing an image of the area or object between the capacitanceplates.
 2. A flexible capacitance sensor according to claim 1, furthercomprised of: a flexible shielding ground layer in between the layer ofcapacitance plates and the plurality of signal traces; a first flexibleisolative layer between the flexible layer of capacitance plates and theflexible shielding ground layer; and a second flexible isolative layerbetween the flexible shielding ground layer and the plurality of signaltraces.
 3. A flexible capacitance sensor according to claim 2, whereinthe first and second flexible isolative layers are resistive forproviding a path to discharge static charges from the flexible layer ofcapacitance plates to the flexible shielding ground layer.
 4. A flexiblecapacitance sensor according to claim 1, further comprised of: aflexible insulation layer for separating the subject being sensed andthe flexible layer of capacitance plates.
 5. A flexible capacitancesensor according to claim 1, further comprised of: a flexible groundlayer for forming an outside layer of the sensor for shielding thesensor from outside interference.
 6. A flexible capacitance sensoraccording to claim 1, wherein the capacitance plates are comprised ofconductive spray on a nonconductive layer.
 7. A flexible capacitancesensor according to claim 1, further comprising a plurality of groundlines placed between the trace lines.
 8. A flexible capacitance sensoraccording to claim 1, wherein all the layers of the flexible capacitancesensor are connected by an adhesive material.
 9. A flexible capacitancesensor according to claim 1, further comprising a plurality of throughholes for providing a path to the plurality of signal traces.
 10. Aflexible capacitance sensor according to claim 1, wherein thecapacitance plates are connected using stretchable connectors.
 11. Aflexible capacitance sensor according to claim 1, wherein thecapacitance plates are applied on an elastic substrate.
 12. A flexiblecapacitance sensor according to claim 11, wherein the conductive sprayor liquid is applied to the elastic substrate to form the capacitanceplates.
 13. A flexible capacitance sensor having multiple layers forcommunicating signals to a data acquisition system for reconstructing animage of an area or object located in a subject being sensed, comprisedof: a flexible layer of capacitance plates; a flexible layer of signaltraces next to the flexible layer of capacitance plates, the layer ofsignal traces having a plurality of trace lines for communicatingsignals from the capacitance plates to the data acquisition system; aflexible insulation layer for separating the subject being sensed andthe flexible layer of capacitance plates; a flexible ground layer forforming an outside layer of the sensor for shielding the sensor fromoutside interference; a plurality of through holes for providing a pathto the flexible layer of signal traces; wherein the capacitance sensoris flexible and adapted to be wrapped around the subject being sensed;wherein the capacitance plates in the flexible layer of capacitanceplates are individually addressable; and wherein the sensor is adaptedto communicate signals to the data acquisition system for use inreconstructing an image of the area or object between the capacitanceplates.
 14. A flexible capacitance sensor according to claim 13, furthercomprised of: a flexible shielding ground layer interposed between theflexible layer of capacitance plates and the flexible layer of signaltraces; a first flexible isolative layer between the flexible layer ofcapacitance plates and the flexible shielding ground layer; and a secondflexible isolative layer between the flexible shielding ground layer andthe flexible layer of signal traces.
 15. A flexible capacitance sensoraccording to claim 14, wherein the first and second flexible isolativelayers are resistive for providing a path to discharge static chargesfrom the flexible layer of capacitance plates to the flexible shieldingground layer.
 16. A flexible capacitance sensor according to claim 13,wherein the capacitance plates are comprised of conductive spray on anonconductive layer.
 17. A flexible capacitance sensor according toclaim 13, wherein the flexible layer of signal traces is furthercomprised of ground lines placed between the trace lines and wherein theplurality of trace lines are in electrical communication with thecapacitance plates.
 18. A flexible capacitance sensor according to claim13, wherein all the layers of the flexible capacitance sensor areconnected by an adhesive material and wherein the capacitance plates arecomprised of conductive metal.
 19. A flexible capacitance sensor made upof a plurality of modular sections each having multiple layers forcommunicating signals to a data acquisition system for reconstructing animage of an area or object located in a subject being sensed, each ofthe modular sections comprised of: a flexible layer of capacitanceplates; a flexible layer of signal traces, the layer of signal traceshaving a plurality of trace lines for communicating signals from thecapacitance plates to the data acquisition system; wherein thecapacitance sensor is flexible and adapted to be wrapped around thesubject being sensed; wherein the capacitance plates in the flexiblelayer of capacitance plates are individually addressable; and whereinthe sensor is adapted to communicate signals to the data acquisitionsystem for use in reconstructing an image of the area or object betweenthe capacitance plates.
 20. A flexible capacitance sensor according toclaim 19, each of the modular sections further comprised of: a flexibleshielding ground layer interposed between the flexible layer ofcapacitance plates and the flexible layer of signal traces; a firstflexible isolative layer between the flexible layer of capacitanceplates and the flexible shielding ground layer; and a second flexibleisolative layer between the flexible shielding ground layer and theflexible layer of signal traces.
 21. A flexible capacitance sensoraccording to claim 19, wherein the sensor is wearable and can be placedat different locations of a human body.
 22. A flexible capacitancesensor according to claim 21, wherein the sensor layers and componentsare made from bio-degradable material for placement inside the humanbody.
 23. A flexible capacitance sensor according to claim 19, whereinthe sensor is made from a combination of rigid and flexible integrativesensing elements formed to image objects subject to expansion.
 24. Acapacitance sensor according to claim 19, further comprising: aplurality of rigid modular portions, wherein the plurality of flexiblemodular sections can be placed onto the plurality of rigid modularportions for placement around a structure being sensed.